Transformers serve an integral role in the delivery of electrical power from generation sources to specific point of use applications. Whether dry-type or liquid-filled, single-phase or three-phase, a wide variety of transformer types are often involved in the transformation of power throughout the electrical system, ultimately providing available power for consumption.
There are many different applications for transformers. The type of transformer utilized for a specific requirement is often dictated by the service conditions and the amount of power required for a particular application. Focusing on liquid-filled transformers only, small residential loads quite often use single-phase transformers mounted overhead or a completely tamperproof version mounted at ground level. Larger commercial or industrial loads could use larger single-phase transformers or could deploy smaller three-phase transformers to reduce the voltage down to usable levels. These products could be overhead, pad mounted (completely tamperproof design), small power type (typically mounted on a concrete pad but must be fenced to prevent public access) or submersible style. Submersible products are often used only in high density load centers where there is insufficient real estate for pad mounted transformer installation. Very large loads require the use of medium power or large power transformers.
Carte International manufactures a broad range of liquid-filled transformer products for the utility, commercial and industrial market sectors primarily within North America.
Certain commercial and industrial loads often require large amounts of electricity and in many cases the users opt to purchase power at a higher voltage and conduct their own voltage transformation, with all the necessary controls and safety aspects such that the power can be purchased at a lower rate. In these cases, switch gear is typically utilized to provide the user the ability to turn the power off and to isolate their load from the electrical system.
Switch gear is comprised of a circuit breaker or a switch which enables the power to be on (or flow through the circuits connected to it) or off (effectively isolating the transformer and any downstream circuits from the electricity source). These switches often have a visible switch mechanism to enable equipment operators to positively see when the breaker (or switch) contacts are open (de-energized) and when they are closed (energized). Switch gear often features a wide variety of control equipment and protective equipment to further enhance the safe operation of the equipment to assist in monitoring power consumption by the user. Fusing and arresters may be included as additional protective equipment in some switch gear designs to guard downstream equipment and components from electrical surges. One of the key aspects of switch gear is that no live high voltage parts are exposed. While switch gear is often not entirely tamperproof, metal enclosures are grounded and mechanical interlocks are often used to prevent inadvertent opening of switch gear compartments which are energized by lesser trained equipment operators.
There are many benefits for closely grouping transformers and switch gear at a commercial or industrial installation as the switch gear is typically closely coupled or attached to the transformer and controls the power that the transformer provides to the site load.
In the early 1990's, Carte embarked a new product line which married basic switch gear with a pad mounted transformer. The resulting product, which is called a Primary Service Entrance Transformer or PSET, is an integrated substation designed for commercial or industrial applications where primary power (at lower rates) is being purchased for consumption. The PSET product concept basically combined the pad mounted transformer with a high voltage fused load break (air-break) disconnect switch all within a tamperproof enclosure. As the product is tamperproof, it may be installed in public access areas and not require a fenced enclosure to contain the equipment.
The high-voltage equipment with the PSET can be operated safely by non-Utility personnel. The design of the PSET has received electrical inspection authority approval (in certain jurisdictions) and, as such, allows the end-user to employ maintenance staff to perform several tasks without having to contact the local electric Utility. One of the key features of the PSET is that the contacts of the air-load break switch must be visible by the operator. In essence, the operator must ensure that the contacts are open prior to any work being done on the equipment or circuits originating from the PSET.
The PSET transformer is physically much smaller than a fenced substation. The PSET requires only a single concrete pad for mounting the equipment versus multiple pads (and perhaps a fenced enclosure) when conventional components are utilized. The PSET is designed to be delivered to the job-site as an integral package that does not require assembly of various component parts.
Because the equipment is packaged direct from the factory, the PSET design offers significant cost savings to the buyer versus a conventional transformer and switch gear arrangement. Size and space requirements at the installation site will be reduced as the typical practice of on-site mating of the transformer and switch gear is eliminated. Site labor is also reduced since the PSET is delivered with all necessary transformer/switch gear interconnections completed.